Prev: Non Sequitur: Re: Python Forum
Next: os.path.normpath question
From: Lie Ryan on 7 Jun 2010 06:20
On 06/07/10 19:31, Richard Thomas wrote:
> On Jun 7, 10:17 am, Peter Otten <__pete...(a)web.de> wrote:
>> Alfred Bovin wrote:
>>> I'm working on something where I need to read a (binary) file bit by bit
>>> and do something depending on whether the bit is 0 or 1.
>>
>>> Any help on doing the actual file reading is appreciated.
>>
>> The logical unit in which files are written is the byte. You can split the
>> bytes into 8 bits...
>>
>>>>> def bits(f):
>>
>> ... while True:
>> ... b = f.read(1)
>> ... if not b: break
>> ... b = ord(b)
>> ... for i in range(8):
>> ... yield b & 1
>> ... b >>= 1
>> ...>>> with open("tmp.dat", "wb") as f: # create a file with some example data
>>
>> ... f.write(chr(0b11001010)+chr(0b10101111))>>> with open("tmp.dat", "rb") as f:
>>
>> ... for bit in bits(f):
>> ... print bit
>> ...
>> 0
>> 1
>> 0
>> 1
>> 0
>> 0
>> 1
>> 1
>> 1
>> 1
>> 1
>> 1
>> 0
>> 1
>> 0
>> 1
>>
>> but that's a very inefficient approach. If you explain what you are planning
>> to do we can most certainly come up with a better alternative.
>>
>> Peter
>
> You're reading those bits backwards. You want to read the most
> significant bit of each byte first...

Of course that depends on the need of the OP?
From: Peter Otten on 7 Jun 2010 06:28
Richard Thomas wrote:

> On Jun 7, 10:17 am, Peter Otten <__pete...(a)web.de> wrote:
>> Alfred Bovin wrote:
>> > I'm working on something where I need to read a (binary) file bit by
>> > bit and do something depending on whether the bit is 0 or 1.
>>
>> > Any help on doing the actual file reading is appreciated.
>>
>> The logical unit in which files are written is the byte. You can split
>> the bytes into 8 bits...
>>
>> >>> def bits(f):
>>
>> ... while True:
>> ... b = f.read(1)
>> ... if not b: break
>> ... b = ord(b)
>> ... for i in range(8):
>> ... yield b & 1
>> ... b >>= 1
>> ...>>> with open("tmp.dat", "wb") as f: # create a file with some example
>> data
>>
>> ... f.write(chr(0b11001010)+chr(0b10101111))>>> with open("tmp.dat",
>> "rb") as f:
>>
>> ... for bit in bits(f):
>> ... print bit
>> ...
>> 0
>> 1
>> 0
>> 1
>> 0
>> 0
>> 1
>> 1
>> 1
>> 1
>> 1
>> 1
>> 0
>> 1
>> 0
>> 1
>>
>> but that's a very inefficient approach. If you explain what you are
>> planning to do we can most certainly come up with a better alternative.
>>
>> Peter
>
> You're reading those bits backwards. You want to read the most
> significant bit of each byte first...
>
> Richard.

>>> def bits(f):
.... while True:
.... byte = f.read(1)
.... if not byte: break
.... byte = ord(byte)
.... for i in reversed(range(8)):
.... yield byte >> i & 1
....
>>> with open("tmp.dat", "rb") as f:
.... for bit in bits(f):
.... print bit,
....
1 1 0 0 1 0 1 0 1 0 1 0 1 1 1 1

From: Nobody on 7 Jun 2010 06:41
On Mon, 07 Jun 2010 02:31:08 -0700, Richard Thomas wrote:

> You're reading those bits backwards. You want to read the most
> significant bit of each byte first...

Says who?

There is no universal standard for bit-order.

Among bitmap image formats, XBM is LSB-first while BMP and PBM are
MSB-first. OpenGL reads or writes bitmap data in either order, controlled
by glPixelStorei().

Most serial communication links (e.g. RS-232, ethernet) transmit the LSB
first, although there are exceptions (e.g. I2C uses MSB-first).

From: Ulrich Eckhardt on 7 Jun 2010 07:20
Nobody wrote:
> On Mon, 07 Jun 2010 02:31:08 -0700, Richard Thomas wrote:
>
>> You're reading those bits backwards. You want to read the most
>> significant bit of each byte first...
>
> Says who?

Says Python:

>>> bin(192)
'0x11000000'

That said, I totally agree that there is no inherently right way and I guess
Richard was just a smiley or two short in order to have correct markup in
his not-so-serious posting.

:^)

Uli

--
Sator Laser GmbH
Geschäftsführer: Thorsten Föcking, Amtsgericht Hamburg HR B62 932

From: Peter Otten on 7 Jun 2010 07:43
Ulrich Eckhardt wrote:

> Nobody wrote:
>> On Mon, 07 Jun 2010 02:31:08 -0700, Richard Thomas wrote:
>>
>>> You're reading those bits backwards. You want to read the most
>>> significant bit of each byte first...
>>
>> Says who?
>
> Says Python:
>
>>>> bin(192)
> '0x11000000'

Hmm, if that's what /your/ Python says, here's mine to counter:

>>> bin(192)
'0_totally_faked_binary_00000011'

;)

Peter
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4
Prev: Non Sequitur: Re: Python Forum
Next: os.path.normpath question